JP6730971B2 - Decontamination apparatus for radioactive metal waste and decontamination method - Google Patents

Description

The technique disclosed in the present specification relates to a decontamination apparatus and a decontamination method for decontaminating radioactive metal waste by electrolytic polishing.

In nuclear power plants and facilities that handle radioactive materials, among the metal waste generated by the abolition, dismantling, or operation of equipment, metal waste with a radioactivity level higher than the standard value (hereinafter referred to as radioactive metal waste Referred to). From the viewpoint of disposal, it is desirable that the surface of these metal wastes be decontaminated to lower the radioactivity level below the standard value before processing. As a decontamination method for radioactive metal waste, a technique for removing the surface of the radioactive metal waste by electrolytic polishing or the like has been developed. For example, in the decontamination apparatus of Patent Document 1, an anode base connected to an anode jig is installed inside a storage tank, and a cylindrical radioactive metal waste is installed above the anode base. The cylindrical radioactive metal waste is installed on the anode stand so that its axial direction is horizontal. Further, a cathode jig is installed in the storage tank, and a cathode is connected to the cathode jig. The cathode is installed so as to axially penetrate the inside of the cylindrical radioactive metal waste. When a voltage is applied between the anode jig and the cathode jig, the surface of the radioactive metal waste is electropolished.

JP-A-3-17600

In the decontamination apparatus as described in Patent Document 1, when a voltage is applied between the anode and the cathode, the metal is dissolved in the electrolytic solution from the radioactive metal waste. Since the dissolved metal gradually adheres to the surface of the cathode, the decontamination ability of the decontamination apparatus decreases with the passage of time. Therefore, when the decontamination ability drops below a preset level, it is necessary to clean the metal deposits attached to the cathode. As a method for cleaning the cathode, for example, a method is known in which a voltage in the opposite direction to that at the time of decontamination is applied to the cathode and the metal deposit attached to the cathode is dissolved again in the electrolytic solution. However, in the decontamination apparatus of Patent Document 1, in order to apply a voltage in the opposite direction to the cathode, the radioactive metal waste and the cathode installed in the storage tank at the time of decontamination are taken out of the storage tank and attached with a metal. The cathode to which the kimono adheres and the electrode that becomes the cathode when a reverse voltage is applied must be reconnected to the power supply device, and these electrodes must be re-installed in the storage tank, resulting in a heavy work load. There was a problem. The present specification discloses a technique for easily cleaning metal deposits attached to an electrode that serves as a cathode during decontamination.

The decontamination apparatus disclosed in this specification decontaminates radioactive metal waste by electrolytic polishing. The decontamination device is a storage tank containing an electrolytic solution, a power supply device, a first electrode that can be arranged in the storage tank, and is electrically connected to the power supply device, and is electrically connected to the power supply device. And a connection member selectively connected to the radioactive metal waste and the second electrode. The connection member has a first position where the radioactive metal waste or the second electrode is arranged inside the storage tank while the first electrode is arranged inside the storage tank, and a radioactive metal waste outside the storage tank. Alternatively, it can be switched to the second position where the second electrode is arranged. The decontamination device is at the first position with the connecting member connected to the radioactive metal waste, and the power supply device is such that the first electrode serves as the cathode and the radioactive metal waste serves as the anode. By applying a voltage, the radioactive metal waste is decontaminated by electrolytic polishing. Further, in the decontamination device, the member connected to the connection member outside the storage tank is treated as a radioactive metal waste by setting the connection member to the second position with the first electrode arranged in the storage tank. Switching to and from the second electrode. Further, the decontamination device is at the first position with the connecting member connected to the second electrode, and the power supply device has the second electrode as the cathode and the first electrode as the anode. By applying the voltage in this manner, the metal deposit attached to the first electrode is washed.

In the above decontamination device, the radioactive metal waste or the second electrode can be selectively connected to the connecting member outside the storage tank by switching the connecting member between the first position and the second position. Therefore, the second electrode can be installed in the storage tank in place of the radioactive metal waste without taking out the first electrode, which serves as the cathode portion during decontamination, from the storage tank. Therefore, the work load for cleaning the first electrode can be reduced, and the first electrode can be easily cleaned.

Further, the decontamination method disclosed in this specification decontaminates radioactive metal waste by electrolytic polishing. The decontamination method includes a first immersion step of immersing a radioactive metal waste electrically connected to a power supply device in an electrolytic solution, a radioactive metal waste immersed in the electrolytic solution by the first immersion step, and an electrolytic solution. A first voltage applying step of applying a forward voltage to a first electrode disposed inside and electrically connected to the power supply device, and a state in which the first electrode is disposed in the electrolytic solution, A step of taking out the radioactive metal waste from the electrolytic solution, a second dipping step of soaking the second electrode electrically connected to the power supply device in the electrolytic solution after the taking out step, a first electrode, and a second electrode A second voltage applying step of applying a reverse voltage to the second electrode immersed in the electrolytic solution by the immersion step.

In the above decontamination method, the radioactive metal waste can be decontaminated by the first voltage application step, and the metal deposit attached to the first electrode can be washed by the second voltage application step. In addition, the radioactive metal waste and the second electrode can be replaced by the taking-out step and the second dipping step without taking out the first electrode from the electrolytic solution. Therefore, the work load for cleaning the first electrode can be reduced, and the first electrode can be easily cleaned.

The figure which shows typically the schematic structure of the decontamination apparatus which concerns on an Example. The perspective view which shows the structure of a fixing jig. The perspective view which shows the structure of a holding jig. It is a top view which shows the structure of a holding part, and shows the state which the holding part is holding the radioactive metal waste. It is a top view which shows the structure of a holding part, and shows the state which the holding part is holding the metal plate. The flowchart which shows an example of the method of decontaminating radioactive metal waste using the decontamination apparatus which concerns on an Example. It is a figure which shows the relationship between the voltage value between an electrode part and a metal plate, and time at the time of cleaning an electrode part, (a) is a voltage value between an electrode part and a metal plate with which the decontamination apparatus of this Example is equipped, and time. And (b) shows the relationship between the voltage value and time between the stainless steel electrode (comparative example) and the metal plate.

The main features of the embodiments described below are listed. The technical elements described below are technical elements that are independent of each other, and exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Absent.

(Feature 1) In the decontamination apparatus disclosed in the present specification, the first electrode may be formed of a metal belonging to the titanium group. According to such a configuration, it is possible to avoid the first electrode itself from being melted when cleaning the metal deposit attached to the first electrode. Therefore, the durability of the first electrode can be improved. Further, when the first electrode is formed of a metal belonging to the titanium group, the first electrode itself is difficult to be dissolved and is attached to the first electrode when cleaning metal deposits attached to the first electrode. The deposited metal deposits dissolve. Therefore, the state of dissolution of the metal deposit on the first electrode can be detected by monitoring the electrical behavior between the first electrode and the second electrode. Therefore, it is possible to avoid an unnecessary lengthening of the cleaning work of the first electrode.

(Feature 2) In the decontamination device disclosed in this specification, the radioactive metal waste may be cylindrical. The connection member may include a grip portion that holds the radioactive metal waste such that the axial direction of the radioactive metal waste is vertical when the connection member is positioned at the first position. According to this structure, when the radioactive metal waste has a cylindrical shape, the radioactive metal waste is stably held in the storage tank by holding the radioactive metal waste by the connecting member. You can

(Feature 3) In the decontamination method disclosed in this specification, the first electrode may be formed of a metal belonging to the titanium group. In the second voltage applying step, the first voltage is applied based on at least one of a voltage applied between the first electrode and the second electrode and a current flowing between the first electrode and the second electrode. The application of the reverse voltage between the second electrode and the second electrode may be stopped. According to such a configuration, since the first electrode is formed of the metal belonging to the titanium group, it is possible to detect the state of dissolution of the deposit attached to the first electrode. Therefore, in the second voltage applying step, it is possible to detect that the cleaning of the first electrode is completed, and it is possible to prevent the cleaning work of the first electrode from being unnecessarily lengthened.

Hereinafter, the decontamination device 10 according to the embodiment will be described. The decontamination device 10 decontaminates a cylindrical radioactive metal waste 2 such as a pipe installed in a nuclear power plant or a facility that handles radioactive substances. In the case of a pipe or the like, a component containing a radioactive substance passes through the inner circumference of the pipe or the like, so that the inner surface thereof is contaminated with the radioactive substance. Therefore, the decontamination apparatus 10 of this embodiment is configured to electrolytically polish the inner surface of the cylindrical radioactive metal waste 2. As shown in FIG. 1, the decontamination device 10 includes a storage tank 12, a power supply device 16, a fixing jig 20 for fixing an electrode part 22 described later, and a holding jig 40 capable of holding the radioactive metal waste 2. Equipped with.

The storage tank 12 has a box shape with an open upper surface. The surface of the storage tank 12 is covered with an insulating material and is insulated from the fixing jig 20 and the holding jig 40. The fixing jig 20 and the holding jig 40 can be inserted into the storage tank 12 from above. The storage tank 12 is filled with the electrolytic solution 14. A filtration device (not shown) is connected to the storage tank 12. The electrolytic solution 14 stored in the storage tank 12 is sent to a filtration device, filtered, and returned to the storage tank 12. That is, the electrolytic solution 14 circulates between the storage tank 12 and the filtering device. As the electrolytic solution 14, a known electrolytic solution used for electrolytic polishing can be used, and for example, an electrolytic solution containing a phosphoric acid solution can be used. In a state where the radioactive metal waste 2 and the electrode portion 22 are immersed in the electrolytic solution 14, the radioactive metal waste 2 is connected to the anode of the power supply device 16, and the electrode portion 22 is connected to the cathode of the power supply device 16 to generate an electric current. When flowing, the surface of the radioactive metal waste 2 is electrochemically dissolved. That is, the metal such as iron forming the surface of the radioactive metal waste 2 and the radioactive substance attached to the surface are dissolved in the electrolytic solution 14.

The fixing jig 20 will be described with reference to FIG. The fixing jig 20 is fixed with an electrode portion 22 serving as a cathode when decontaminating the radioactive metal waste 2. By arranging the fixing jig 20 in the storage tank 12, the electrode portion 22 is arranged in the storage tank 12. As shown in FIG. 2, the fixing jig 20 includes a plurality of electrode portions 22, a lower plate 24, a frame 28, a connecting portion 36, and a guide portion 38. The surfaces of the lower plate 24, the frame 28, and the guide portion 38 are covered with an insulating material so that these surfaces are not electropolished. The guide portion 38 may be made of a non-conductive material so that the surface thereof is not electrolytically polished.

The electrode portion 22 has a rod shape and is made of titanium. Since the electrode portion 22 is made of titanium, it is possible to prevent the electrode portion 22 itself from being dissolved in the electrolytic solution 14 together with the attached metal when cleaning the metal attached to the electrode portion 22. Although the electrode portion 22 of this embodiment is made of titanium, it is not limited to such a structure. For example, the electrode portion 22 may be formed of a metal belonging to the titanium group such as zirconium. The electrode portion 22 is installed on the lower plate 24 perpendicularly to the lower plate 24 (in the Z direction in FIG. 2 ). A plurality of electrode portions 22 are arranged on the lower plate 24, and the dimensions of the plurality of electrode portions 22 in the height direction (that is, the Z direction) are substantially the same. In this embodiment, 10 electrode portions 22 are arranged in 5×2 rows. Specifically, five electrode portions 22 are arranged on a straight line extending in the X direction, and the remaining five electrode portions 22 are arranged at positions substantially equidistant from each other in the Y direction. Has been done. In addition, in the present embodiment, the fixing jig 20 is provided with ten electrode portions 22, but the number of electrode portions 22 is not particularly limited, and may be more than 10, or more than 10. May be small. Moreover, the electrode part 22 is an example of a "1st electrode."

The lower plate 24 has a substantially rectangular flat plate shape in plan view and is made of stainless steel. The size of the lower plate 24 in the X direction is larger than the size in the Y direction. On the upper surface of the lower plate 24, ten electrode portions 22 are vertically fixed upward. As described above, the lower plate 24 is made of stainless steel and the electrode portion 22 is made of titanium. Therefore, the electric charges flowing in the lower plate 24 flow from the lower plate 24 to the electrode portion 22. Further, the lower plate 24 is provided with a plurality of through holes 26. The through hole 26 has an arc shape, and the two through holes 26 are arranged at positions surrounding one electrode portion 22. As will be described later, when the radioactive metal waste 2 is placed in the storage tank 12, the electrode portion 22 is located inside the inner circumference of the radioactive metal waste 2. The through hole 26 is formed so as to be located between the electrode portion 22 and the inner circumference of the radioactive metal waste 2 when the radioactive metal waste 2 is placed in the storage tank 12 and viewed in a plan view. By providing the through hole 26 in the lower plate 24, the electrolytic solution 14 can pass through the through hole 26 and be appropriately circulated between the radioactive metal waste 2 and the electrode portion 22.

The frame 28 is made of stainless steel and has four sides 30 and an upper portion 32. The side portion 30 has a plate shape extending in the Z direction, and has a lower end connected to the lower plate 24 and an upper end connected to the upper portion 32. More specifically, the lower end of the side portion 30 is bent at a substantially right angle so as to be parallel to the lower plate 24, and the bent portion is joined to the lower plate 24. When viewed in a plan view, the upper ends of the side portions 30 project outward (in the Y direction in FIG. 2) from the lower plate 24 and are bent at a substantially right angle so as to be parallel to the upper portion 32. When viewed in a plan view, the X-direction dimension of the outer circumferences of the side portion 30 and the lower plate 24 is smaller than the X-direction dimension of the inner circumference of the storage tank 12, and the Y dimension of the outer circumferences of the side portion 30 and the lower plate 24 is reduced. The dimension in the direction is smaller than the dimension in the Y direction of the inner circumference of the storage tank 12. Therefore, when the fixing jig 20 is installed in the storage tank 12, the side portion 30 and the lower plate 24 are arranged in the storage tank 12.

The upper portion 32 is arranged on the upper portion of the fixing jig 20, and is joined to the four side portions 30. The upper part 32 is arranged parallel to the lower plate 24. The upper portion 32 has a substantially rectangular outer circumference and a substantially rectangular inner circumference having a constant width from the outer circumference. The inner circumference of the upper portion 32 is sized to substantially match the outer circumference of the lower plate 24 when seen in a plan view. Therefore, when viewed along the X direction, the upper portion 32 projects from the lower plate 24 toward the +Y direction side and the −Y direction side. Further, the upper portion 32 projects from the lower plate 24 and the side portion 30 toward the +X direction side and the −X direction side when viewed along the Y direction. A recess 34 is provided in the upper portion 32 near the center of the portion extending along the Y direction. The concave portion 34 has a shape that engages with a support portion 72 of the holding jig 40 described later. Since the surface of the recess 34 is covered with an insulating material, the upper portion 32 (that is, the fixing jig 20) and the supporting portion 72 (that is, the holding jig 40) are not electrically connected. ..

Four connecting portions 36 are connected to the upper portion 32, and two connecting portions 36 are arranged at a position projecting from the upper portion 32 toward the +X direction side and two at a position protruding from the upper portion 32 toward the −X direction side in a plan view. Are arranged. In other words, the connecting portions 36 are arranged on both sides of the two recesses 34 and project outside the upper portion 32. When the fixing jig 20 is installed in the storage tank 12, the four connecting portions 36 are in contact with the upper surface of the storage tank 12. Further, the connecting portion 36 is electrically connected to the power supply device 16. The charges flowing from the power supply device 16 flow in the order of the connection portion 36, the upper portion 32, the side portion 30, and the lower plate 24, and then flow from the lower plate 24 to the electrode portion 22. Therefore, when the cathode of the power supply device 16 and the connection part 36 are connected, the electrode part 22 functions as a cathode, and when the anode of the power supply device 16 and the connection part 36 are connected, the electrode part 22 functions as an anode. In this embodiment, the four connecting portions 36 contact the upper surface of the storage tank 12 when the fixing jig 20 is installed in the storage tank 12, but the upper portion 32 (specifically, in the Y direction of the upper portion 32). The portion that extends along) may contact the upper surface of the storage tank 12.

Two guide portions 38 are installed on the lower plate 24 perpendicularly to the lower plate 24 (that is, in the Z direction). The two guide portions 38 are arranged in the vicinity of the corners of the lower plate 24 at diagonal positions, and more specifically, in the vicinity of the corners of the lower plate 24 in the +X direction and the −Y direction, and in the −X direction and. It is arranged at two places near the corner in the +Y direction. The guide portion 38 is used to position the holding jig 40. In this embodiment, the guide portion 38 is arranged near the two corners of the lower plate 24, but the configuration is not limited to such a configuration. It suffices that the holding jig 40 can be positioned by the guide portion 38, the arrangement position of the guide portion 38 is not limited, and the shape of the guide portion 38 is not limited. The number of guide portions 38 is not limited, and may be one or three or more.

The holding jig 40 will be described with reference to FIGS. 3 to 5. The holding jig 40 selectively holds the radioactive metal waste 2 or the metal plate 4 and can be installed in the fixing jig 20. The holding jig 40 is an example of a “connecting member”. As shown in FIG. 3, the holding jig 40 includes a mounting portion 42, a grip portion 50, a frame 70, a support portion 72, and a take-out portion 76. The surfaces of the mounting portion 42, the frame 70, and the take-out portion 76 are covered with an insulating material. The take-out portion 76 may be made of a non-conductive material.

The mounting part 42 is disposed below the holding jig 40 and mounts the radioactive metal waste 2 or the metal plate 4. The mounting portion 42 includes a bottom portion 44, a side portion 46, and a guide portion 48.

The bottom portion 44 has a substantially rectangular outer periphery when viewed in a plan view, and the outer periphery size is smaller than the inner periphery size of the upper portion 32. The bottom portion 44 has members arranged in a lattice shape, and the electrode portions 22 pass between the lattices when the holding jig 40 is arranged in the fixing jig 20. Since the bottom portion 44 has a lattice shape, the electrolytic solution 14 can pass between the lattices provided on the bottom portion 44. Therefore, when the holding jig 40 is taken out of the storage tank 12, the amount of the electrolytic solution 14 taken out of the storage tank 12 together with the holding jig 40 can be reduced. Although the size of the grid provided on the bottom portion 44 is not particularly limited, when the radioactive metal waste 2 or the metal plate 4 is placed on the bottom portion 44, the size does not allow the radioactive metal waste 2 and the metal plate 4 to pass through. Is preferred. Further, in the present embodiment, the bottom portion 44 has a lattice shape, but if the structure is such that the electrode portion 22 and the electrolytic solution 14 can pass through and the radioactive metal waste 2 or the metal plate 4 can be placed. Well, for example, the bottom portion 44 may be a plate material (for example, punching metal) provided with a plurality of through holes, or a mesh member.

The side portion 46 has a plate shape and is connected to the bottom portion 44 and a connecting portion 68 described later. The side portions 46 are connected to both ends of the bottom portion 44 on the X direction side and are installed perpendicularly to the bottom portion 44. The lower portion of the side portion 46 is joined to the bottom portion 44, and the plate width thereof gradually decreases from the lower side to the upper side. The connecting portion 68 is joined to the upper end side of the side portion 46.

The guide portion 48 projects to the outside of the bottom portion 44, and in this embodiment, projects to the +X direction side and the −X direction side (not shown) of the bottom portion 44. The guide portion 48 is provided with a guide hole 48a. The guide hole 48 a has a size that allows the rod-shaped guide portion 38 to pass therethrough, and is arranged at a position corresponding to the guide portion 38. That is, the guide hole 48 a is arranged at a position where the guide portion 38 penetrates when the holding jig 40 is installed in the fixing jig 20. Since the fixing jig 20 includes the guide portion 38 and the holding jig 40 includes the guide hole 48a, the holding jig 40 can be installed at an appropriate position in the fixing jig 20.

The grip part 50 selectively grips the radioactive metal waste 2 or the metal plate 4. The grip portion 50 is arranged between the two side portions 46. The grip portion 50 includes a first member 52, a second member 62, and a connecting portion 68 fixed to the side portion 46. The radioactive metal waste 2 or the metal plate 4 is arranged between the first member 52 and the second member 62. The surface of the gripping portion 50 other than the portion in contact with the radioactive metal waste 2 or the metal plate 4 is covered with an insulating material so that these surfaces are not electropolished.

The first member 52 has a substantially rectangular parallelepiped shape and is made of stainless steel. The first member 52 extends in the X direction, and a plurality of grooves 54 are provided on both side surfaces extending along the X direction. The grooves 54 extend in the Z direction, and in this embodiment, three grooves are provided on the side surface of the first member 52 on the −Y direction side, and three grooves are provided on the side surface of the first member 52 on the +Y direction side. ing. As shown in FIG. 4, the groove 54 includes side surfaces 56a and 56b that are perpendicular to the side surface 52a extending along the X direction of the first member 52 (that is, parallel to the YZ plane), and parallel to the side surface 52a and the side surface 56a. A side surface 58 perpendicular to 56b (that is, parallel to the XZ plane) is provided.

The groove 54 is located at a position where the electrode portion 22 coincides with the central portion of the side surface 58 (central portion in the X direction) when viewed along the Y direction with the holding jig 40 installed in the fixing jig 20. It is provided. In this embodiment, when viewed along the Y direction, the groove 54 is provided at a position corresponding to the six electrode portions 22 arranged in the center among the ten electrode portions 22, and the grooves 54 are provided at both ends. The groove 54 is not provided at a position corresponding to the electrode portion 22 of the book. The position and the number of the grooves 54 are not particularly limited, and can be appropriately set according to the position and the number of the radioactive metal waste 2 held by the holding jig 40. That is, the groove 54 may be provided at a position corresponding to the electrode portion 22 where the radioactive metal waste 2 is arranged, and the number of the groove 54 is not limited. The dimensions of the side surfaces 56 a, 56 b, 58 are determined according to the size of the radioactive metal waste 2. In detail, the dimensions of the side surfaces 56 a, 56 b, 58 are such that when the radioactive metal waste 2 is arranged at a position in contact with the first member 52, the radioactive metal waste 2 and the first member 52 have both edges of the groove 54. The dimensions are such that they only contact the portions 60a and 60b (that is, the edges that are the boundaries between the side surface 52a and the side surfaces 56a and 56b). Such a size of the groove 54 allows the radioactive metal waste 2 to engage with the groove 54 and stably hold the radioactive metal waste 2. Further, since the radioactive metal waste 2 does not contact the side surface 58 of the groove 54, the contact portion between the radioactive metal waste 2 and the first member 52 can be reduced.

That is, if the dimensions of the side surfaces 56a and 56b in the Y direction are too small, the depth (dimension in the Y direction) of the groove 54 becomes shallow, and the radioactive metal waste 2 contacts the side surface 58. Then, the number of contact points between the radioactive metal waste 2 and the first member 52 increases. If the size of the side surface 58 is too small, it becomes difficult for the radioactive metal waste 2 to engage with the groove 54, and the radioactive metal waste 2 cannot be stably held. If the size of the side surface 58 is too large, the radioactive metal waste 2 is contained in the groove 54 and does not come into contact with both edges 60a and 60b of the groove 54. Therefore, the radioactive metal waste 2 does not engage with the groove 54, and the radioactive metal waste 2 cannot be stably held. By providing the groove 54 having the above-described configuration in the first member 52, the radioactive metal waste 2 can be stably held. Further, since the contact portion between the radioactive metal waste 2 and the first member 52 is reduced, the electrolytic solution 14 is kept between the radioactive metal waste 2 and the first member 52 when the holding jig 40 is taken out from the storage tank 12. It becomes difficult to stay, and the amount of the electrolytic solution 14 carried out of the storage tank 12 can be reduced. In particular, in the present embodiment, the radioactive metal waste 2 contacts only the both edges 60a, 60b of the groove 54, so that the clearance between the radioactive metal waste 2 and the first member 52 in the vicinity of the contact portion is wide. be able to. As a result, the amount of the electrolytic solution 14 held between the radioactive metal waste 2 and the first member 52 can be reduced due to the surface tension of the electrolytic solution 14. Thereby, the amount of the electrolytic solution 14 carried out of the storage tank 12 can be reduced appropriately.

The first member 52 is detachably installed on the connecting portion 68 fixed to the side portion 46. Holding the radioactive metal waste having a diameter different from that of the radioactive metal waste 2 and the metal plate 4 of various sizes by the holding jig 40 by changing the type of the first member attached to the connecting portion 68. You can

The second member 62 has a substantially rectangular flat plate shape, and is arranged parallel to the first member 52 in the X direction and separated from the first member 52 in the Y direction. One second member 62 is arranged on the +Y direction side and one second member 62 on the −Y direction side. Each second member 62 is connected to the first member 52 by a bolt 64. Two bolts 64 are arranged for each second member 62, and one bolt 1 is provided near each end of the first member 52 (that is, an end on the +X direction side and an end on the −X direction side). They are arranged one by one. By adjusting the screw amount of the bolt 64 into the first member 52, the distance between the first member 52 and the second member 62 can be adjusted.

Either the radioactive metal waste 2 or the metal plate 4 is arranged between the second member 62 and the first member 52. By tightening the bolt 64, the radioactive metal waste 2 or the metal plate 4 is sandwiched between the first member 52 and the second member 62. When disposing the radioactive metal waste 2 between the second member 62 and the first member 52, hold one to six radioactive metal wastes 2 in accordance with the position where the groove 54 is provided. You can

As shown in FIGS. 4 and 5, when arranging the metal plate 4 between the second member 62 and the first member 52, one sheet is provided on each of the +Y direction side and the −Y direction side of the first member 52. The metal plate 4 is arranged. The metal plate 4 has a substantially rectangular plate shape and is made of stainless steel. The dimension of the metal plate 4 in the X direction is shorter than the distance between the two bolts 64 that connect each second member 62 to the first member 52. Therefore, the metal plate 4 can be arranged between the second member 62 and the first member 52 while being placed on the bottom portion 44. Further, as shown in FIG. 5, the plate thickness (dimension in the Y direction) of the metal plate 4 is between the first member 52 and the electrode portion 22 when the holding jig 40 is installed in the fixing jig 20. In addition, the metal plate 4 and the second member 62 are sized so as to fit therein. Therefore, the dimension of the metal plate 4 in the Y direction is smaller than the dimension of the radioactive metal waste 2 in the Y direction. By making the distance between the first member 52 and the second member 62 smaller than the case where the radioactive metal waste 2 is arranged by the screwing amount of the bolt 64, the first member 52 and the second member 62 are separated from each other. The metal plate 4 can be held between them, and the metal plate 4 and the first member 52 (specifically, the side surface 52a) can be electrically connected. The metal plate 4 is an example of the “second electrode”.

Further, a cushioning material 66 is arranged on the surface of the second member 62 facing the first member 52. Even if there is an error in the diameter of the radioactive metal wastes 2 (three in this embodiment) arranged between the second member 62 and the first member 52 due to the buffer material 66, a plurality of radioactive metal wastes All two can be held stably.

The frame 70 is made of stainless steel and extends long in the Z direction. The frame 70 is connected to the connecting portion 68, and the two frames 70 are connected to the connecting portion 68 arranged on the −X direction side and the connecting portion 68 arranged on the +X direction side, respectively.

The support portion 72 has a plate shape extending in the X direction and is made of stainless steel. The dimension of the support portion 72 in the X direction is the dimension of the fixing jig 20 in the X direction (that is, in the fixing jig 20, from the connecting portion 36 installed in the −X direction to the connecting portion 36 installed in the +X direction. Length)). The dimension of the support portion 72 in the Y direction is smaller than the dimension of the entire holding jig 40 in the Y direction, and is a dimension that engages with the recess 34. The support portion 72 is arranged above the holding jig 40 and at a position substantially in the center of the holding jig 40 in the Y direction. The support portion 72 is connected to the frame 70 and projects toward the +X direction side and the −X direction side of the frame 70. Note that, as described above, the support portion 72 and the recess 34 of the fixing jig 20 are insulated.

At both ends of the support portion 72, connection portions 74 that are electrically connected to the power supply device 16 are arranged. The electric charge flowing from the power supply device 16 flows in the order of the supporting portion 72, the frame 70, the connecting portion 68, and the first member 52. Then, when the radioactive metal waste 2 is arranged in the grip portion 50, the charges flowing in the first member 52 flow in the radioactive metal waste 2. Further, when the metal plate 4 is arranged on the grip portion 50, the electric charge that has flowed to the first member 52 flows to the metal plate 4.

When the radioactive metal waste 2 is arranged in the grip portion 50, the anode of the power supply device 16 and the connection portion 74 are connected. Then, the radioactive metal waste 2 functions as an anode. When the holding jig 40 is installed in the storage tank 12 with the radioactive metal waste 2 arranged in the grip portion 50, the electrode portion 22 is inserted into the inner circumference of the radioactive metal waste 2. In this state, when the fixing jig 20 is connected to the cathode of the power supply device 16 and the holding jig 40 is connected to the anode of the power supply device 16, an electric current is generated between the electrode portion 22 and the inner surface of the radioactive metal waste 2. As the metal flows, the metal is dissolved in the electrolytic solution 14 from the inner surface of the radioactive metal waste 2. That is, together with the metal forming the inner surface of the radioactive metal waste 2, the radioactive substance attached to the surface is dissolved in the electrolytic solution 14. As a result, the inner surface of the radioactive metal waste 2 can be decontaminated. When the decontamination process is continued, the metal dissolved in the electrolytic solution 14 gradually adheres to the surface of the electrode portion 22.

On the other hand, when the metal plate 4 is arranged on the grip portion 50, the cathode of the power supply device 16 and the connecting portion 74 are connected. Then, the metal plate 4 functions as a cathode. When the holding jig 40 is installed in the storage tank 12 with the metal plate 4 placed on the grip 50, the metal plate 4 and the electrode portion 22 face each other. In this state, when the fixing jig 20 is connected to the anode of the power supply device 16 and the holding jig 40 is connected to the cathode of the power supply device 16, a current flows between the electrode portion 22 and the metal plate 4. Then, the metal attached to the surface of the electrode portion 22 is dissolved in the electrolytic solution 14. By such decontamination treatment, the metal attached to the surface of the electrode portion 22 can be washed.

In addition, in the present embodiment, the metal plate 4 is gripped by the grip portion 50 using the first member 52 and the second member 62 used when gripping the radioactive metal waste 2, but such a configuration is used. Not limited. The metal plate 4 is electrically connected to the power supply device 16 and is held by the holding jig 40, and when the holding jig 40 is installed in the fixing jig 20, the metal plate 4 faces the electrode portion 22. It may be arranged at a position. For example, a dedicated first member and a second member for gripping the metal plate 4 may be installed on the holding jig 40 to hold the metal plate 4 on the holding jig 40. However, if the radioactive metal waste 2 or the metal plate 4 is selectively held by using the same first member 52 and second member 62, it is not necessary to manufacture a plurality of types of first member 52 and second member 62. .. Therefore, the manufacturing cost can be suppressed, and the space for storing the plurality of types of the first member and the second member can be reduced. Further, the shape of the metal member that serves as a cathode when cleaning the electrode portion 22 is not limited to the plate shape extending along the X direction. For example, the metal member that serves as a cathode when cleaning the electrode portion 22 may be a plate material that extends in the Y direction. For example, when the holding jig 40 is placed in the fixing jig 20, a plurality of metal plates are held by the gripping portion 50 so that they are located between the adjacent electrode portions 22 and separate the adjacent electrode portions 22. May be. Further, the metal member that serves as a cathode when cleaning the electrode portion 22 may have a cylindrical shape.

The take-out portion 76 is a plate material that extends in the Y direction and is connected to the upper surface of the support portion 72. A protrusion 78 is attached to the upper portion of the take-out portion 76. The entire holding jig 40 can be taken out of the storage tank 12 by gripping the protrusion 78 and lifting it up by a crane (not shown). Therefore, only the holding jig 40 can be taken out from the storage tank 12 while the fixing jig 20 is arranged in the storage tank 12. Further, the take-out portion 76 is installed above the guide hole 48a, and the take-out portion 76 is provided with a guide hole 80 at a position corresponding to the guide hole 48a when seen in a plan view. Therefore, when the holding jig 40 is housed in the fixing jig 20, the guide portion 38 penetrates the guide hole 48a and further penetrates the guide hole 80. By providing the guide hole 80, the holding jig 40 can be arranged at an appropriate position. Although the guide hole 80 is provided in the take-out portion 76 in the present embodiment, it is not limited to such a configuration. The guide hole 80 may be provided at a position corresponding to the guide hole 48a in plan view, and may be provided in a member other than the takeout portion 76.

In the decontamination apparatus 10 of this embodiment, the radioactive metal waste 2 and the metal plate 4 can be selectively installed on the holding jig 40. Further, only the holding jig 40 can be taken out without taking out the fixing jig 20. Therefore, the radioactive metal waste 2 and the metal plate 4 installed on the holding jig 40 can be replaced with each other without taking out the electrode portion 22 functioning as a cathode from the storage tank 12 during decontamination. Therefore, the work load for cleaning the electrode portion 22 can be reduced.

Next, with reference to FIG. 6 and FIG. 7, a method for decontaminating the radioactive metal waste 2 using the decontamination apparatus 10 of the present embodiment will be described. In the decontamination device 10, the radioactive metal waste 2 is decontaminated and the metal (hereinafter, also referred to as a metal deposit) attached to the electrode portion 22 by the decontamination process is washed.

As shown in FIG. 6, first, the radioactive metal waste 2 is installed on the holding jig 40 (S12). Installation of the radioactive metal waste 2 on the holding jig 40 is performed by the following procedure. First, outside the storage tank 12, the first member 52 suitable for the diameter of the radioactive metal waste 2 to be decontaminated is attached to the holding jig 40. Then, the radioactive metal waste 2 is placed on the placing section 42. At this time, the side surface of the radioactive metal waste 2 is placed at a position in contact with the edge portions 60a and 60b of the groove 54. As described above, since the first member 52 is provided with the grooves 54 at six places, six radioactive metal wastes 2 are placed in accordance with the positions of the grooves 54. The number of radioactive metal wastes 2 to be placed may be less than six. After mounting the radioactive metal waste 2 on the mounting portion 42, the position of the second member 62 is adjusted so that the radioactive metal waste 2 is held between the first member 52 and the second member 62. Then, the radioactive metal waste 2 is installed on the holding jig 40.

Next, the holding jig 40 in which the radioactive metal waste 2 is installed in step S12 is placed in the storage tank 12 (S14). An electrolytic solution 14 is stored in the storage tank 12, and a fixing jig 20 is further arranged. The holding jig 40 is arranged in the fixing jig 20 arranged in the storage tank 12. Specifically, the holding jig 40 is inserted into the fixing jig 20 while penetrating the two guide portions 38 into the guide holes 48a. Further, the two guide portions 38 are respectively passed through the guide holes 80, and the support portions 72 are engaged with the recesses 34. In this way, the holding jig 40 is arranged in the fixing jig 20. When the holding jig 40 is placed in the fixing jig 20, the electrode portion 22 is located inside the inner circumference of the radioactive metal waste 2. In addition, step S14 is an example of a "1st immersion process."

Next, the connection portion 36 of the fixing jig 20 is connected to the cathode of the power supply device 16, the connection portion 74 of the holding jig 40 is connected to the anode of the power supply device 16, and the connection portion 36 between the two connection portions 36, 74 is connected. A voltage is applied (S16). Then, a voltage is applied between the electrode portion 22 and the inner surface of the radioactive metal waste 2, and the metal is dissolved in the electrolytic solution 14 from the inner surface of the radioactive metal waste 2 that functions as an anode. As a result, the inner surface of the radioactive metal waste 2 is decontaminated. At this time, the metal dissolved in the electrolytic solution 14 gradually adheres to the surface of the electrode portion 22 that functions as a cathode. Note that step S16 is an example of the “first voltage applying step”.

When the inner surface of the radioactive metal waste 2 is decontaminated, the holding jig 40 is taken out of the storage tank 12 (S18). At this time, the holding jig 40 can be taken out while the fixing jig 20 is arranged in the storage tank 12. Specifically, the protrusion 78 is gripped by a crane (not shown), and the holding jig 40 is lifted upward. Then, only the holding jig 40 is taken out of the storage tank 12. It should be noted that step S18 is an example of a “removal step”.

Next, the radioactive metal waste 2 is removed from the holding jig 40, and the metal plate 4 is placed on the holding jig 40 (S20). The installation of the metal plate 4 on the holding jig 40 is performed by the following procedure. First, the bolt 64 is adjusted to separate the second member 62 from the first member 52. Then, the radioactive metal waste 2 is removed from the holding jig 40. Then, the metal plate 4 is mounted on the mounting part 42. At this time, the metal plate 4 is placed at a position where one surface of the metal plate 4 contacts the side surface 52a of the first member 52. Then, the position of the second member 62 is adjusted so that the metal plate 4 is fixed between the first member 52 and the second member 62. Then, the metal plate 4 is held by the holding jig 40.

Next, the holding jig 40 having the metal plate 4 installed in step S20 is placed in the storage tank 12 (S22). Since step S22 is the same procedure as step S14, detailed description thereof will be omitted. When the holding jig 40 is arranged in the fixing jig 20, the electrode portion 22 and the metal plate 4 face each other. Note that step S22 is an example of the “second immersion step”.

Next, the connecting portion 36 of the fixing jig 20 is connected to the anode of the power supply device 16, the connecting portion 74 of the holding jig 40 is connected to the cathode of the power supply device 16, and the two connecting portions 36, 74 are connected to each other. A voltage is applied (S24). That is, in step S24, a voltage in the opposite direction to that in step S16 is applied. Then, a voltage is applied between the electrode part 22 and the metal plate 4, and the metal deposit on the surface of the electrode part 22 functioning as an anode is dissolved in the electrolytic solution 14. As a result, the surface of the electrode portion 22 is cleaned.

When the voltage is applied, the voltage value applied between the electrode portion 22 and the metal plate 4 is measured (S26). Here, the voltage value between the electrode portion 22 and the metal plate 4 when the electrode portion 22 is cleaned will be described with reference to FIG. 7. FIG. 7A shows the relationship between the voltage value between the electrode portion 22 and the metal plate 4 and the time when the electrode portion 22 is cleaned. FIG. 7B shows, as a comparative example, the relationship between the voltage value between the stainless steel electrode and the metal plate 4 and the time during cleaning of the electrode portion formed of stainless steel (hereinafter, also referred to as stainless steel electrode). There is. In this embodiment, a constant current source is used for the power supply device 16.

When a voltage is applied between the electrode portion 22 and the metal plate 4, the metal deposit on the surface of the electrode portion 22 dissolves, while the electrode portion 22 formed of titanium does not dissolve. Therefore, as shown in FIG. 7A, when a constant current flows between the electrodes, as the metal deposit attached to the surface of the electrode portion 22 is dissolved in the electrolytic solution 14, the electrode portion 22 and the metal plate 4 are separated from each other. The electric resistance between them gradually increases. Therefore, the voltage applied between the electrode portion 22 and the metal plate 4 also rises. When almost all the metal deposits on the surface of the electrode part 22 are dissolved, the electric resistance between the electrode part 22 and the metal plate 4 becomes constant, and the voltage value of the voltage applied between both becomes constant. Therefore, by measuring the voltage value between the electrode portion 22 and the metal plate 4, it is possible to detect the state of dissolution of the metal deposit on the surface of the electrode portion 22. On the other hand, when a voltage is applied between the stainless steel electrode and the metal plate 4, the metal deposit on the surface of the stainless steel electrode is dissolved and the stainless steel electrode itself is also dissolved. Therefore, as shown in FIG. 7(b), when a constant current flows between the electrodes, the stainless steel electrode itself continues to dissolve even after all the metal deposits are dissolved, so that the electric resistance becomes substantially constant, and the voltage value also increases. It becomes almost constant. Therefore, even if the voltage value between the stainless electrode and the metal plate 4 is measured, it is not possible to detect the state of dissolution of the metal deposit on the surface of the stainless electrode.

Next, it is determined whether or not the voltage value measured in step S26 is greater than or equal to the threshold value (S28). As described above, when almost all metal deposits on the surface of the electrode portion 22 are dissolved, the voltage value becomes substantially constant. Therefore, in this embodiment, the threshold value is set based on the voltage value when almost all the metal deposits are dissolved. For example, in the example shown in FIG. 7A, the threshold value can be set to 20V. Therefore, by determining whether or not the measured voltage value has reached the threshold value, it can be determined that the dissolution of the metal deposit adhered to the surface of the electrode portion 22 is completed. When the voltage value does not reach the threshold value (NO in step S28), it is determined that all the metal deposits attached to the electrode portion 22 are not dissolved, and the process returns to step S26, and the voltage is applied until the voltage value reaches the threshold value. The cleaning process is continued while continuing to measure the value. When the voltage value is equal to or higher than the threshold value (YES in step S28), it is determined that the metal attached to the electrode portion 22 has been melted, the voltage application is stopped, and the cleaning process is ended. By monitoring the voltage value in this way, it is possible to avoid an unnecessary lengthening of the cleaning process time. Note that steps S24 to S28 are an example of the “second voltage applying step”.

In the decontamination method using the decontamination apparatus 10 of the present embodiment, the radioactive metal waste 2 is held without taking out the fixing jig 20 that fixes the electrode portion 22 functioning as a cathode during decontamination from the storage tank 12. The holding jig 40 can be taken out of the storage tank 12. Therefore, the metal plate 4 can be placed in the storage tank 12 instead of the radioactive metal waste 2 while the electrode portion 22 is placed in the storage tank 12. Therefore, when performing the cleaning process of the electrode portion 22, it is not necessary to take out the electrode portion 22 from the storage tank 12, and the work load can be reduced.

In this embodiment, the voltage value is measured in step S26, but the present invention is not limited to such a configuration. It is only necessary to be able to detect the state of dissolution of metal deposits on the surface of the electrode portion 22, and for example, a constant voltage source may be used in the power supply device to measure the current value between the electrode portion 22 and the metal plate 4. In this case, the electric resistance between the electrode portion 22 and the metal plate 4 increases as the metal deposit dissolves, so that the current value of the current flowing between the both decreases. Then, when almost all the metal deposits on the surface of the electrode portion 22 are dissolved, the electric resistance between the electrode portion 22 and the metal plate 4 becomes constant, so that the current value also becomes constant. Therefore, by measuring the current value flowing between the electrode portion 22 and the metal plate 4, it is possible to detect the state of dissolution of the metal deposit on the surface of the electrode portion 22.

Further, in the decontamination method of the present embodiment, the cleaning process of the electrode part 22 is performed every time the decontamination process of the radioactive metal waste 2 is completed, but the configuration is not limited to such a configuration. For example, the cleaning process of the electrode part 22 may be performed after it is determined that a large amount of metal deposit adheres to the surface of the electrode part 22 and the decontamination ability is lowered below a certain level. That is, after the decontamination process of the radioactive metal waste 2 is completed, another decontamination process of the radioactive metal waste 2 may be repeatedly performed, and when the decontamination capacity is lowered, the electrode part 22 may be cleaned. ..

In addition, in this embodiment, the inner surface of the cylindrical radioactive metal waste 2 is electrolytically polished by using the decontamination device 10, but the invention is not limited to such a configuration. For example, a flat radioactive metal waste may be installed on the holding jig 40 and the surface of the flat radioactive metal waste may be electrolytically polished.

The specific examples of the technology disclosed in the present specification have been described above in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. Further, the technical elements described in the present specification or the drawings exert technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

2: Radioactive metal warehouse waste 4: Metal plate 10: Decontamination device 12: Storage tank 14: Electrolyte 16: Power supply device 20: Fixing jig 22: Electrode part 24: Lower plate 38: Guide part 40: Holding jig 48a : Guide hole 50: Gripping portion 52: First member 60a, 60b: Edge portion 62: Second member 66: Cushioning material 80: Guide hole

Claims (6)

A decontamination device for decontaminating radioactive metal waste by electrolytic polishing,
A storage tank containing an electrolyte,
Power supply,
A first electrode that can be placed in the reservoir,
A fixing member that is electrically connected to the power supply device and that fixes the first electrode;
A connection member electrically connected to the power supply device and selectively connected to the radioactive metal waste and the second electrode;
The connection member has a first position in which the radioactive metal waste or the second electrode is arranged in the storage tank, with the first electrode being arranged in the storage tank, and the storage member. It is possible to switch to the second position where the radioactive metal waste or the second electrode is arranged outside the tank,
The connecting member is disposed in the fixing member when being in the first position,
The connection member is set to the first position in a state of being connected to the radioactive metal waste, and the power supply device has the first electrode as a cathode and the radioactive metal waste as an anode. By applying a voltage to, decontamination of the radioactive metal waste by electrolytic polishing,
By setting the connecting member to the second position in a state in which the first electrode is arranged in the storage tank, a member connected to the connecting member outside the storage tank is connected to the radioactive metal waste and the second member. Switch between 2 electrodes,
The connection member is set to the first position in a state of being connected to the second electrode, and the power supply device has the second electrode as a cathode and the first electrode as an anode. A decontamination device for cleaning a metal deposit attached to the first electrode by applying a voltage to the first electrode. The decontamination device according to claim 1, wherein the second electrode is a metal plate. The connection member includes a first member and a second member,
The decontamination device according to claim 1 or 2, wherein the radioactive metal waste or the second electrode is sandwiched between the first member and the second member. It said first electrode is formed by a metal belonging to titanium group, decontamination apparatus according to any one of claims 1-3. The radioactive metal waste is cylindrical,
The connection member includes a grip portion that holds the radioactive metal waste such that an axial direction of the radioactive metal waste is a vertical direction when the connection member is positioned at the first position. Item 5. The decontamination device according to any one of items 1 to 4 . A decontamination method for decontaminating radioactive metal waste by electrolytic polishing,
A first dipping step of dipping the radioactive metal waste electrically connected to a power supply device in an electrolyte solution;
A forward voltage is applied to the radioactive metal waste immersed in the electrolytic solution by the first immersion step and a first electrode disposed in the electrolytic solution and electrically connected to the power supply device. A first voltage applying step of applying
A step of taking out the radioactive metal waste from the electrolytic solution with the first electrode placed in the electrolytic solution;
A second dipping step of dipping a second electrode electrically connected to the power supply device in an electrolytic solution after the extracting step;
A second voltage applying step of applying a reverse voltage to the first electrode and the second electrode immersed in the electrolytic solution by the second immersion step ,
The first electrode is formed of a metal belonging to the titanium group,
In the second voltage applying step, at least one of a voltage applied between the first electrode and the second electrode and a current flowing between the first electrode and the second electrode. The decontamination method of stopping the application of the voltage in the opposite direction between the first electrode and the second electrode based on the above .

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